Author name code: frutiger ADS astronomy entries on 2022-09-14 author:"Frutiger, C." ------------------------------------------------------------------------ Title: Fundamental parameters and granulation properties of Alpha Centauri A and B obtained from inversions of their spectra Authors: Frutiger, C.; Solanki, S. K.; Mathys, G. Bibcode: 2005A&A...444..549F Altcode: Properties of stellar granulation are obtained by inverting spectra of the late-type stars α Centauri A and B. Our inversions are based on a multi-component model of the stellar photosphere and take into account the center-to-limb variation and rotational broadening. The different atmospheric components describe the areas harboring up-, down- and horizontal flows. The inversions are constrained by fitting not only the flux profiles, but also their line bisectors, and by using a simple mass conservation scheme. The inversions return the properties of convection at the stellar surface, including the stratification of the thermodynamic parameters, as well as fundamental parameters such as the gravitational acceleration, v sin i and the element abundances. For α Cen A (G2V) the derived stratifications of the temperature and convective velocity are very similar to the Sun, while for α Cen B (K1V) we find similar up- and downflow velocities, but lower horizontal speeds and a reduced overshoot. The latter is consistent with the smaller scale height of the atmosphere, while mass conservation arguments taken with the lower horizontal speed imply that the granules on α Cen B are smaller than on the Sun. Both these properties are in good agreement with the hydrodynamic simulation of Nordlund & Dravins (1990, A&A, 228, 155). The inversions also return the fundamental parameters (T_eff, log g, abundances, v sin i, etc.) of the two stars. These values are on the whole in good agreement with literature values. Also, most of them do not strongly depend on the details of the inversion. However, importantly, the element abundances are 0.1 to 0.15 dex lower when a 2- or 3-component inversion is carried out than with a 1-component inversion.

Based on observations collected at the European Southern Observatories, La Silla, Chile. Title: The molecular Zeeman effect and diagnostics of solar and stellar magnetic fields. II. Synthetic Stokes profiles in the Zeeman regime Authors: Berdyugina, S. V.; Solanki, S. K.; Frutiger, C. Bibcode: 2003A&A...412..513B Altcode: Recent advances in the computation of the Zeeman splitting of molecular lines have paved the way for their use as diagnostics of solar and stellar magnetic fields. A systematic study of their diagnostic capabilities had not been carried out so far, however. Here we investigate how molecular lines can be used to deduce the magnetic and thermal structure of sunspots, starspots and cool stars. First, we briefly describe the Stokes radiative transfer of Zeeman-split molecular lines. Then, we compute Stokes spectra of TiO, OH, CH and FeH lines and investigate their diagnostic capabilities. We also compare the synthetic profiles with observations. Spectra of TiO, OH and FeH are found to be interesting diagnostics of sunspot magnetic fields. This is also true for cool stars, where, however, the OH Stokes V profiles may require very high S/N data to be reliably employed. Finally we investigate the potential of various molecular bands for high-contrast imaging of the solar surface. The violet CN and CH bands turn out to be most promising for imaging the photosphere, the TiO bands are excellent for imaging sunspot umbrae, while the UV OH band can be used for imaging both the photosphere and sunspots. Title: Three dimensional structure of a regular sunspot from the inversion of IR Stokes profiles Authors: Mathew, S. K.; Lagg, A.; Solanki, S. K.; Collados, M.; Borrero, J. M.; Berdyugina, S.; Krupp, N.; Woch, J.; Frutiger, C. Bibcode: 2003A&A...410..695M Altcode: The magnetic, thermal and velocity structure of a regular sunspot, observed close to solar disk center is presented. Spectropolarimetric data obtained with the Tenerife Infrared Polarimeter (TIP) in two infrared FeI lines at 15 648.5 Å and 15 652.8 Å are inverted employing a technique based on response functions to retrieve the atmospheric stratification at every point in the sunspot. In order to improve the results for the umbra, profiles of Zeeman split OH lines blending the FeI 15 652.8 Å are also consistently fit. Thus we obtain maps of temperature, line-of-sight velocity, magnetic field strength, inclination, and azimuth, as a function of both location within the sunspot and height in the atmosphere. We present these maps for an optical depth range between log tau5 = 0 and log tau5 = -1.5, where these lines provide accurate results. We find decreasing magnetic field strength with increasing height all over the sunspot, with a particularly large vertical field gradient of ~ -4 G km-1 in the umbra. We also observe the so called ``spine'' structures in the penumbra, i.e. extended radial features with a stronger and more vertical magnetic field than the surroundings. Also we found that the magnetic field zenith angle increases with height. From the velocity map it is clear that the Evershed flow avoids the spines and mostly concentrates in the more inclined intervening field. The field inclination at a few locations in the outer penumbra in lower layers goes beyond 90o. These locations coincide with the strongest flows in the velocity map. Title: Structure of a simple sunspot from the inversion of IR spectral data Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Collados, M.; Berdyugina, S. V.; Frutiger, C.; Krupp, N.; Woch, J. Bibcode: 2003AN....324..388M Altcode: Analysis of spectral data of two neighboring infrared lines, Fe i 15648.5 Å (g = 3) and Fe i 15652.9 Å (g_eff = 1.53) are carried out for a simple sunspot when it was near the solar disk center (mu = 0.92), to understand the basic structure of sunspot magnetic field. Inversions of Stokes profiles are carried out to derive different atmospheric parameters both as a function of location within the sunspot and height in the atmosphere. As a result of the inversion we have obtained maps of magnetic field strength, temperature, line-of-sight velocity, field inclination and azimuth for different optical depth layers between log (tau_ {5}) = 0 and log (tau_ {5}) = -2.0 . In this paper we present few results from our inversion for a layer averaged between log (tau_ {5}) from 0.0 to -0.5. Title: Magnetic Elements Near the Solar Limb: Inversions Based on a Flux-tube Model Authors: Frutiger, C.; Solanki, S. K.; Gandorfer, A. Bibcode: 2003ASPC..307..344F Altcode: No abstract at ADS Title: Modeling the Fine Structure of a Sunspot Penumbra through the Inversion of Stokes Profiles Authors: Borrero, J. M.; Lagg, A.; Solanki, S. K.; Frutiger, C.; Collados, M.; Bellot Rubio, L. R. Bibcode: 2003ASPC..286..235B Altcode: 2003ctmf.conf..235B No abstract at ADS Title: Thermal-magnetic relation of a sunspot as inferred from the inversion of 1.5 μm spectral data Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Krupp, N.; Woch, J.; Collados, M.; Berdyugina, S.; Frutiger, C. Bibcode: 2002ESASP.505..501M Altcode: 2002IAUCo.188..501M; 2002solm.conf..501M We present the thermal-magnetic relation in a simple, isolated sunspot deduced from the inversion of 1.56 μm spectropolarimetric data. Due to the high Zeeman sensitivity of the g = 3, Fe I 1.5648 μm line, we can study this relationship in the entire sunspot. An inversion technique based on response functions is used to derive various parameters, both as a function of location within the sunspot and of height in the atmosphere. In this paper we attempt to relate field strength, vertical and radial field components and the field inclination with temperature. Title: Modelling solar irradiance variations: separate models for the network and active region faculae Authors: Wenzler, T.; Solanki, S. K.; Fluri, D. M.; Frutiger, C.; Fligge, M.; Ortiz, A. Bibcode: 2002ESASP.508..231W Altcode: 2002soho...11..231W In order to determine to what extent solar surface magnetism affects solar irradiance we need to reconstruct the irradiance from magnetograms. This process requires the use of model atmospheres. Here we present two model atmospheres describing faculae in active regions and the network. The models have been constructed such that they reproduce various data sets simultaneously. Title: Empirical models of solar magnetic flux-tubes and their non-magnetic surroundings Authors: Frutiger, C.; Solanki, S. K. Bibcode: 2001A&A...369..646F Altcode: A powerful method for the analysis of the structure of small scale magnetic elements in the solar photosphere is the inversion of Stokes spectra. In previous papers based on such inversions \cite{BellotRubio:etal:1997, BellotRubio:etal:1999} and \cite{Frutiger:etal:1999} have argued in favor of models with rather different dynamic properties. In this paper we return to this debate and compare results returned by inversions based on new multi-component models applied to several Fe i, Fe ii and C i spectral line profiles obtained in active region plage with a Fourier Transform Spectrometer. These inversions differ from earlier ones by the fact that mass conservation is strictly imposed both inside the magnetic elements and on the surrounding external flow field. These flux-tube models are not only able to reproduce the characteristic Stokes V asymmetries and line-shifts observed in active regions plages or network elements, but also the Stokes I line profiles, including line bisectors. It is confirmed that from the quality of the fits alone it is not possible to distinguish between the steady flow proposed by \cite{BellotRubio:etal:1997} and the oscillatory model of \cite{Frutiger:Solanki:1998}. If, however, physical constraints are imposed (e.g. mass conservation or that the flow retains the same direction over height in the flux tube) then the oscillatory model is found to be superior. In addition, the current investigation also provides the first inversion-based model of abnormal granulation. Title: The Formation of One-Lobed Stokes V Profiles in an Inhomogeneous Atmosphere Authors: Ploner, S. R. O.; Schussler, M.; Solanki, S. K.; Sheminova, V. A.; Gadun, A. S.; Frutiger, C. Bibcode: 2001ASPC..236..371P Altcode: 2001aspt.conf..371P We assess the diagnostic potential of the observed pathological Stokes V profiles that differ strongly from the customary, nearly antisymmetric two-lobed shape. In particular, we consider the formation of one-lobed Stokes V profiles using the results of an MHD simulation. We find that the majority of one-lobed profiles is produced in regions of weak horizontal field with significant cancellation caused by mixed polarity along the line of sight. A minority of one-lobed profiles originates close to strong magnetic field concentrations with strong gradients of velocity and magnetic field strength. Title: Consistent Empirical Models of Solar Magnetic Flux Tubes and the Surrounding Convection (CD-ROM Directory: contribs/frutige2) Authors: Frutiger, C.; Solanki, S. K. Bibcode: 2001ASPC..223..632F Altcode: 2001csss...11..632F No abstract at ADS Title: Magnetic Splitting of Molecular Lines in Sunspot Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K. Bibcode: 2001IAUS..203..254B Altcode: A study of molecular lines in sunspots is of particular interest because of their high temperature and pressure sensitivity. Many of them are also magnetically sensitive, but this was not yet widely investigated. With high-resolution, high signal-to-noise Fourier spectroscopy in four Stokes parameters now available, the use of molecular lines for studying the structure of sunspots brings real gains. One is the extension of spot models, including magnetic field, up to layers, where atomic lines suffer from NLTE effects but molecules can still be treated in the LTE approximation. Equally important is the fact that since molecular lines are extremely temperature sensitive they can be used to probe the thermal and magnetic structure of the coolest parts of sunspots. We present calculations of splitting and the Stokes parameters for a number of molecular lines in the visible and near-infrared regions. Our first selections are the green system of MgH A2Π-X2σ and the TiO triplet α, γ' and γ systems as the most studied band systems in the sunspot spectrum. The calculations involve different regimes of the molecular Zeeman effect, up to the complete Paschen-Back effect for individual lines. We look for molecular lines which can be used along with atomic lines to derive magnetic, thermal and dynamic properties of the umbra. Title: The Molecular Zeeman Effect and Solar Magnetic Fields Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K.; Livingston, W. Bibcode: 2001ASPC..236..551B Altcode: 2001aspt.conf..551B No abstract at ADS Title: Solar and Stellar Magnetic Fields: the Molecular Zeeman Effect as a Probe Authors: Berdyugina, S. V.; Solanki, S. K.; Frutiger, C. Bibcode: 2001ASPC..248...99B Altcode: 2001mfah.conf...99B No abstract at ADS Title: Empirical Models of Stellar Convection (CD-ROM Directory: contribs/frutige1) Authors: Frutiger, C.; Solanki, S. K. Bibcode: 2001ASPC..223..626F Altcode: 2001csss...11..626F No abstract at ADS Title: Successful spectral synthesis of Zeeman-split molecular bands in sunspot spectra Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K.; Livingstone, W. Bibcode: 2000A&A...364L.101B Altcode: We present the first spectral synthesis of Zeeman-split Stokes profiles of the MgH A2Pi -X2BLAigma green system and TiO gamma -system. The calculations involve different regimes of the molecular Zeeman effect, up to the complete Paschen-Back effect for individual lines. The synthetic spectra are compared with observations of Stokes I and V in sunspot umbrae. We find that although the Stokes I spectra are reasonably reproduced, some lines are obviously still missing from the employed line lists. The Stokes V spectra turn out to be much cleaner since the missing lines do not appear to be Zeeman-split. We thus provide the first good fit to Zeeman-split molecular lines, including profiles with unconventional Stokes V shapes, determined by the Paschen-Back effect. Based on observations from the Canada-France-Hawaii Telescope operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France and the University of Hawaii Title: Properties of the solar granulation obtained from the inversion of low spatial resolution spectra Authors: Frutiger, C.; Solanki, S. K.; Fligge, M.; Bruls, J. H. M. J. Bibcode: 2000A&A...358.1109F Altcode: The spectra of cool stars are rich in information on elemental abundances, convection and non-thermal heating. Extracting this information is by no means straightforward, however. Here we demonstrate that an inversion technique may not only provide the stratification of the classical parameters describing a model atmosphere, but can also determine the properties of convection at the stellar surface. The inversion technique is applied to spectra of photospheric lines, one recorded at the quiet solar disk center, the other integrated over the whole disk. We find that a model based on a single plane-parallel atmosphere gives unsatisfactory fits to the spectral lines and suffers from considerable uncertainties in the derived temperature stratification. Also, the elemental abundances returned by the inversion are not particularly reliable. These problems are greatly reduced if two atmospheric components, corresponding to granular up- and downflows are allowed for. The best results are obtained if the line profiles and bisectors of a neutral and ionized species are fit and the results are constrained using a simple mass conservation scheme. We find that inversions based on two- and three-component models of disk-integrated spectra give similar results to inversions of disk-center observations, although with somewhat lower accuracy. This similarity is promising for future applications of line profile inversions to the study of late-type stars and in particular their convection. Title: Inversion of Stokes profiles Authors: Frutiger, C.; Solanki, S. K.; Fligge, M.; Bruls, J. H. M. J. Bibcode: 1999ASSL..243..281F Altcode: 1999sopo.conf..281F No abstract at ADS Title: Infrared lines as probes of solar magnetic features. XIV. TI i and the cool components of sunspots Authors: Rueedi, I.; Solanki, S. K.; Keller, C. U.; Frutiger, C. Bibcode: 1998A&A...338.1089R Altcode: The first systematic observations of sunspot umbrae using the lines of the Ti Ii multiplet at 2.2 mu m are presented. Their diagnostic capabilities are investigated, developed and used to investigate the magnetic and velocity structure of a sunspot. These lines are most sensitive to cool plasma. In addition, they are extremely Zeeman sensitive. We find that a sunspot is composed of two distinct cool magnetic components. One of them is fairly vertical, has a large magnetic field strength and is associated with the central (umbral) part of the sunspot. The other component is strongest near the outer boundary of the spot (penumbra), is much more inclined, has a very low magnetic field strength and shows the signature of the Evershed effect. In contrast to the smooth transition of field strength from the darkest part of the umbra to the outer penumbral boundary usually visible in observations carried out in other spectral lines, the Ti Ii lines exhibit a sharp transition between the two magnetic components. Title: Do solar magnetic elements harbor downflows? Authors: Frutiger, C.; Solanki, S. K. Bibcode: 1998A&A...336L..65F Altcode: In a recent paper Bellot Rubio et al. (1997) inverted Zeeman split Stokes profiles to infer the stratification of the temperature, velocity and magnetic field in the photospheric layers of solar magnetic elements (modeled as thin flux tubes). One controversial result of their inversions is the presence of a strong downflow within the flux tubes. In the model underlying their inversion such a downflow is necessary to reproduce the asymmetric shape of the observed V profiles. We present inversions based on two different flux-tube models, both of which reproduce the Stokes I and V profiles obtained in plages and the network with high accuracy, including the V profile asymmetry. One model is almost identical to that employed by Bellot Rubio et al. (1997), and results in a significant downflow within the flux tube. The other, although similar in most respects, has mass conservation enforced inside the flux tubes, i.e. they contain both an upflow and a downflow which could arise from oscillations or siphon flows. Hence, current data may not be sufficiently sensitive to distinguish between the two velocity structures, so that there is no compelling evidence for a net downflow of matter inside magnetic elements. From a physical point of view the model incorporating mass conservation is to be preferred.